With the continuous development of intelligent terminals, information transfer and interaction methods are becoming increasingly diversified. Compared with Bluetooth, infrared data transmission, wireless network, or other near field communication methods, sound waves, as a near field communication method, have advantages, such as, strong real-time performance, no external network connections required, no high configuration required, no particular requirements, simple, and convenient. Therefore, data transmission over sound waves methods are widely applied.
The patent application with Publication No. CN102291205B discloses a high-reliability data transmission method and apparatus based on multi-frequency sound waves. The method carries out data transmission by using a loudspeaker and a microphone of an existing terminal. At a sending end, a check value of transmitted data is calculated by employing a Cyclic Redundancy Check (CRC) method, and complete data is mapped to a band of 16 KHz to 22 KHz according to a frequency mapping rule. Then, PCM coding is carried out to send multi-frequency sound wave information in the form of sine waves, till the transmission is completed or time is out. At a receiving end, if a multi-frequency sound wave signal meets a length requirement, based on a corresponding decoding rule, complete audio information is divided into a corresponding number of time segments according to a single frequency duration length, and amplitudes of frequencies in each time segment are calculated and sorted. A frequency with maximum amplitude is a preferred frequency of the time segment, and others are alternative frequencies. Next, values corresponding to preferred frequencies in respective time segments are used to form a group of complete data, and a? check is carried out. If the check is successful, the data transmission is completed; if the check fails, a maximum alternative frequency is used, and another check is performed, until the check succeeds. Otherwise, an information start bit is shifted backwards by one time length (which is 1/n of a single frequency duration length) for storage, and check is performed again.
It can be learned through analysis that, the existing data transmission methods over sound waves have the following disadvantages:
1) The communication distance is short. Since a waveform sent by the sending end is a sine signal, spectrum leakage occurs easily in such a baseband signal. During transmission, since energy is not centralized enough, a sound wave transmission distance is severely limited. In addition, in frequency switching, a difference between frequencies easily causes noise.
2) The identification accuracy is low. At the receiving end, as energy of a sent sound wave signal is not centralized, the amplitude of sound waves would be very small especially at a long distance. Meanwhile, noise interference would be severe, and a relatively large error occurs easily in frequency discrimination, and the identification accuracy is also decreased significantly.
In conclusion, the existing data transmission methods over sound waves have problems of a short communication distance and low identification accuracy.